This invention relates generally to rotary shaft decoupling devices, and more particularly to a novel and improved shaft decoupler which enables interrupting the transmission of torque between a prime mover such as an engine and a driven accessory such as a pump.
A variety of techniques have been employed in existing shaft disconnect mechanisms, all of which suffer from reliability problems, maintainability problems and other aspects that make them undesirable. One type of shaft disconnect in wide use is the "guillotine" type in which a solid rotating shaft is fractured by impact (shear rupture) with a plunger thrust into the plane of rotation of an eccentric lobe or cam. That device, although quite simple, and therefore reliable, causes maintenance problems when it is actuated because of the severity of the impact and the necessity to replace a number of rather expensive parts.
A second disconnect type in wide use consists of a face gear arrangement, also called a curvic coupling, which is caused to separate or disconnect by sliding one half of the gear set axially away from the other half. When the gear teeth no longer mesh one half (the driven half) of the coupling ceases rotation. A major problem with this class of disconnects is wear of the loaded metal surfaces such as the gear teeth and bearing surfaces. As wear due to fretting progresses, a build-up of oxidized wear debris inhibits the sliding motion often times preventing the coupling from disconnecting when called upon. The wear also progressses at times to the extent that the coupling fails during service causing a disconnect inadvertently. This leads to a hazardous situation since it occurs unannounced and results in the inflight loss of an important propulsion subsystem such as a generator or pump. This second category of disconnect design also accounts for a large number of maintenance problems due to the complexity of the design and the need for higher level maintenance attention.
Other existing disconnect designs differ somewhat in the method of decoupling, but exhibit the same basic failings due to wear and the related damage during disconnect. They also share the same safety hazard potential, unreliability and requirement for frequent, higher level maintenance.